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目录
哨兵的作用和工作原理
服务状态监控
选举新的 master
如何实现故障转移
搭建哨兵集群
哨兵的作用和工作原理
Redis 提供了哨兵 (Sentinel) 机制来实现主从集群的自动故障恢复。哨兵的结构和作用如下
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监控：Sentinel 会不断检查你的 master 和 slave 是否按预期工作
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自动故障恢复：如果 master 故障， Sentinel 会将一个 Slave 提成为 master ，当故障实例恢复后也还是以新的 master 为主
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通知：Sentinel 充当 Redis 客户端的服务发现来源，当集群发生故障转移时，会将最新消息推送至 Redis 客户端
服务状态监控
Sentinel 基于心跳机制检测服务状态，每隔 1 秒向集群的每个实例发送ping 命令
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主管下线：如果某 Sentinel 节点发现某实例未在规定时间内响应，则认为该实例主观下线
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客观下线：若超过指定数量（quorum）的 sentinel 都认为该实例主观下线，则该实例客观下线。quorum 值最好超过 Sentinel 实例数量的一半
选举新的 master
一旦发现 master 故障，sentinel 需要在 slave 中选择一个作为新的 master ：
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首先会判断 slave 节点与 master 节点断开的时间长短，如果超出指定值 （down-after-milliseconds * 10）则会排除该 slave 节点
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然后判断 slave 节点的 slave-priority 值，越小优先级越高，如果是 0 则永远不参与选举
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如果 slave-prority 一样，则判断 slave 节点的 offset 值，越大说明数据越新，优先级越高
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最后是判断 slave 节点的运行 id 大小，越小优先级越高
如何实现故障转移
当选中了其中一个 slave 为新的 master 后，故障的转移的步骤如下
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sentinel 给备选的 slave 节点发送 slaveof no one 命令，让该节点成为 master
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sentinel 给所有其他 slave 发送 slaveof 192.168.142.152 6379 命令，让这些 slave 成为新的 master 的从节点，开始从新的 master 上同步数据
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最后，sentinel 将故障节点标记为 slave ，当故障节点恢复后会自动成为新的 master 的 slave 节点
搭建哨兵集群
| IP | PORT | ROLE |
|---|---|---|
| 192.168.142.157 | 6379 | master |
| 192.168.142.156 | 6379 | slave |
| 192.168.142.155 | 6379 | slave02 |
| 192.168.142.157 | 26379 | sentinel |
| 192.168.142.156 | 26379 | sentinel |
| 192.168.142.155 | 26379 | sentinel |
我这里省事，只用了三台服务
master , sentinel
docker-compose.yml
services:redis-master:image: hub.atomgit.com/amd64/redis:7.0.13restart: alwayscontainer_name: redis-masterprivileged: trueports:- '6379:6379'volumes:- redis-data:/opt/bitnami/redis/data- /root/redis.conf:/etc/redis.conf- /etc/localtime:/etc/localtime:rocommand:- /bin/sh- -c- redis-server /etc/redis.confredis-sentinel:image: hub.atomgit.com/amd64/redis:7.0.13restart: alwayscontainer_name: redis-sentinelprivileged: trueports:- '26379:26379'volumes:- /root/sentinel.conf:/etc/sentinel.conf- /etc/localtime:/etc/localtime:rocommand:- /bin/sh- -c- redis-server /etc/sentinel.conf --sentinel
volumes:redis-data:
redis.conf
daemonize no
port 6379
protected-mode no
bind 0.0.0.0
requirepass 123456
sentinel.conf
port 26379
protected-mode no
sentinel monitor mymaster 192.168.142.157 6379 2
sentinel auth-pass mymaster 123456
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 3000
slave , sentinel
docker-compose.yml
services:redis-slave:image: hub.atomgit.com/amd64/redis:7.0.13restart: alwayscontainer_name: redis-slaveprivileged: trueports:- '6379:6379'volumes:- redis-data:/opt/bitnami/redis/data- /root/redis.conf:/etc/redis.conf- /etc/localtime:/etc/localtime:rocommand:- /bin/sh- -c- redis-server /etc/redis.confredis-sentinel:image: hub.atomgit.com/amd64/redis:7.0.13restart: alwayscontainer_name: redis-sentinelprivileged: trueports:- '26379:26379'volumes:- /root/sentinel.conf:/etc/sentinel.conf- /etc/localtime:/etc/localtime:rocommand:- /bin/sh- -c- redis-server /etc/sentinel.conf --sentinel
volumes:redis-data:
redis.conf
daemonize no
port 6379
protected-mode no
masterauth 123456
requirepass 123456
slave-read-only yes
bind 0.0.0.0
slaveof 192.168.142.157 6379
sentinel.conf
port 26379
protected-mode no
sentinel monitor mymaster 192.168.142.157 6379 2
sentinel auth-pass mymaster 123456
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 3000slave02 , sentinel
docker-compose.yml
services:redis-slave02:image: hub.atomgit.com/amd64/redis:7.0.13restart: alwayscontainer_name: redis-slave02privileged: trueports:- '6379:6379'volumes:- redis-data:/opt/bitnami/redis/data- /root/redis.conf:/etc/redis.conf- /etc/localtime:/etc/localtime:rocommand:- /bin/sh- -c- redis-server /etc/redis.confredis-sentinel:image: hub.atomgit.com/amd64/redis:7.0.13restart: alwayscontainer_name: redis-sentinelprivileged: trueports:- '26379:26379'volumes:- /root/sentinel.conf:/etc/sentinel.conf- /etc/localtime:/etc/localtime:rocommand:- /bin/sh- -c- redis-server /etc/sentinel.conf --sentinel
volumes:redis-data:
redis.conf
daemonize no
port 6379
protected-mode no
masterauth 123456
requirepass 123456
slave-read-only yes
bind 0.0.0.0
slaveof 192.168.142.157 6379
sentinel.conf
port 26379
protected-mode no
sentinel monitor mymaster 192.168.142.157 6379 2
sentinel auth-pass mymaster 123456
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 3000
哨兵就盯着 master 看，一旦 master g了就立刻预警，就可以开始启动 docker 了
启动 docker
在三台主机上分别执行
docker compose up -d
查看状态 Up 表示成功启动
root@master:~# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
aa6466e6fa15 hub.atomgit.com/amd64/redis:7.0.13 "docker-entrypoint.s…" 27 minutes ago Up 21 minutes 6379/tcp, 0.0.0.0:26379->26379/tcp, :::26379->26379/tcp redis-sentinel
27a2f19d8040 hub.atomgit.com/amd64/redis:7.0.13 "docker-entrypoint.s…" 27 minutes ago Up 21 minutes 0.0.0.0:6379->6379/tcp, :::6379->6379/tcp redis-master
root@slave:~# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1d3df2c507f5 hub.atomgit.com/amd64/redis:7.0.13 "docker-entrypoint.s…" 25 minutes ago Up 21 minutes 6379/tcp, 0.0.0.0:26379->26379/tcp, :::26379->26379/tcp redis-sentinel
b9b981917f2d hub.atomgit.com/amd64/redis:7.0.13 "docker-entrypoint.s…" About an hour ago Up 21 minutes 0.0.0.0:6379->6379/tcp, :::6379->6379/tcp redis-slave
root@slave02:~# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
774fb813bbf2 hub.atomgit.com/amd64/redis:7.0.13 "docker-entrypoint.s…" 23 minutes ago Up 20 minutes 6379/tcp, 0.0.0.0:26379->26379/tcp, :::26379->26379/tcp redis-sentinel
02a276c8edc8 hub.atomgit.com/amd64/redis:7.0.13 "docker-entrypoint.s…" About an hour ago Up 20 minutes 0.0.0.0:6379->6379/tcp, :::6379->6379/tcp redis-slave02
启动成功就可以去查看 sentinel 的状态了
root@master:~# docker exec redis-sentinel redis-cli -p 26379 -c info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_tilt_since_seconds:-1
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=192.168.142.157:6379,slaves=2,sentinels=1
root@slave:~# docker exec -it redis-sentinel redis-cli -p 26379 -c info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_tilt_since_seconds:-1
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=192.168.142.157:6379,slaves=0,sentinels=1
root@slave02:~# docker exec -it redis-sentinel redis-cli -p 26379 -c info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_tilt_since_seconds:-1
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=192.168.142.157:6379,slaves=0,sentinels=1
出现本机 ip 和 ok 状态就代表哨兵启动成功
测试
假设 master 宕机
root@master:~# docker stop redis-master查看 slave
root@slave:~# docker exec redis-slave redis-cli -a 123456 -c role
slave
192.168.142.157
6379
connect
-1
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
查看 slave02
root@slave02:~# docker exec -it redis-slave02 redis-cli -a 123456 -c role
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
1) "master"
2) (integer) 19487
3) 1) 1) "192.168.142.156"2) "6379"3) "19347"
到此，哨兵搭建完成
补充
关于 sentinel.conf 讲解
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sentinel monitor mymaster 192.168.142.157 6379 2 指定主节点信息
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mymaster 主节点名称，自定义
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192.168.142.157 6379 主节点 IP 和端口
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2 选举 master 时的 quorum 值
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sentinel down-after-milliseconds mymaster 5000 salve 与 master 断开的超时时间
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sentinel failover-timeout mymaster 60000 故障恢复的超时时间
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sentinel auth-pass mymaster 123456 主节点密码
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sentinel parallel-syncs mymaster 1
这条指令告诉 Sentinel，对于名为mymaster的 Redis 主节点，在进行故障转移时，只允许一个从节点同时对新的主节点进行数据同步。这意味着在故障转移过程中，只有一个从节点会开始与新的主节点同步数据，其他从节点会等待，直到该从节点完成同步后才开始。设置
parallel-syncs为 1 可以确保在故障转移期间，只有一个从节点在任何给定时间与新的主节点进行数据同步。这样做的好处是可以减少对新主节点的负载，避免在故障转移期间对新主节点造成过大的压力，从而影响其性能。然而，这也意味着故障转移过程可能会花费更长的时间，因为从节点需要一个接一个地进行数据同步。